The present invention relates to an ultrasound diagnostic apparatus and an ultrasound image producing method and particularly to an ultrasound diagnostic apparatus and an ultrasound image producing method for measuring an intima-media complex thickness of blood vessels.
Conventionally, ultrasound diagnostic apparatuses for use in ultrasound diagnosis utilizing ultrasound images have been put in a practical use in medicine. In general, this type of ultrasound diagnostic apparatus comprises an ultrasound probe having a built-in transducer array and an apparatus body connected to the ultrasound probe. The ultrasound probe transmits ultrasonic waves toward a subject, receives ultrasonic echoes from the subject, and the apparatus body electrically processes reception signals from the probe to produce an ultrasound image.
Such an ultrasound diagnostic apparatus may acquire various kinds of information indicative of the status of disease based on reception signals obtained by receiving ultrasonic echoes from the subject. For example, in order to acquire information on circulatory diseases such as arteriosclerosis and cerebral infarction, ultrasonic waves are transmitted to and received from a blood vessel, and the resulting reception signals are used to measure the intima-media complex thickness (IMT) of the blood vessel wall and the like. The value of intima-media complex thickness varies with the progression of arteriosclerosis, so that the status of a circulatory disease can be estimated by observing the value.
However, since vascular wall thickness is thin, and the pulsation associated with heartbeat causes noises to be mixed in reception signals, it has been difficult to accurately measure the intima-media complex thickness of vascular walls.
To cope with it, as a technique to accurately measure the intima-media complex thickness of vascular walls, an ultrasound diagnostic apparatus that detects a boundary of intima-media complex based on a gradient of intensity distribution of a sound ray signal and an amount of change in the intensity to thereby calculate the intima-media complex thickness, is proposed as disclosed by, for example, JP 2008-168016 A.
In the ultrasound diagnostic apparatus described in JP 2008-168016 A, a threshold value used in evaluating an amount of change in the brightness represented by sound ray signals is set, and when a boundary of intima-media complex is not detected, the threshold value is gradually lowered as well as gradually decreasing a search range, whereby the intima-media complex thickness of a blood vessel can be measured with the intima-media complex being distinguished from the noise.